David Kahn, 93; cracked the code of cryptology

David Kahn, a journalist and historian who unlocked the hidden world of cryptology in his best-selling 1967 book “The Codebreakers” and became a preeminent scholar of signals intelligence, revered even among the keepers of the secrets he revealed, died Jan. 23 at his home in the Bronx. He was 93.

The cause was complications from a stroke in 2015, according to his family.

Dr. Kahn was 13 and was passing by his local library in Great Neck, N.Y., when he noticed a book called “Secret and Urgent: The Story of Codes and Ciphers” by military historian Fletcher Pratt. The title alone “stopped me in my tracks,” Dr. Kahn said years later.

Fascinated by the intrigue contained in the book’s pages, he became an amateur cryptologist — a person concerned with cryptography, or the making of codes, and cryptanalysis, or the breaking of them — and maintained the interest beyond boyhood into his career as a newspaperman.

Dr. Kahn was working for Newsday on Long Island in 1960 when two mathematicians employed by the National Security Agency, William H. Martin and Bernon F. Mitchell, defected to the Soviet Union and laid bare the communications-gathering activities of the NSA. Among other charges, they claimed the United States had cracked the codes of 40 other countries, including numerous allies.

Located at Fort Meade, Md., the NSA was — and remains — so secretive that its acronym has long been joked to stand for “No Such Agency.” Amid the clamor surrounding the defection, the New York Times commissioned Dr. Kahn to write a freelance magazine article explaining the history of cryptology. The article became the germ of his first and best-known book.

“The Codebreakers,” billed as “the first comprehensive history of secret communication from ancient times to the threshold of outer space,” was an immediate sensation.

In more than 1,000 pages of prose that was both authoritative and readable, and with no security clearance to ease his research, Dr. Kahn carried the reader through thousands of years of history— from the age of cuneiform writing through the deciphered Zimmermann telegram of World War I and code breaking in World War II to the activities of the NSA.

“Nobody wrote about this stuff,” said Nicholas Reynolds, the author of “Need to Know: World War II and the Rise of American Intelligence.” “He opened the door to a whole new field, basically, the history of signals intelligence.”

It was a door that many US government officials wished to remain closed. James Bamford, a journalist who has written extensively on American intelligence, has described the steps the NSA considered taking to block the publication of Dr. Kahn’s work or limit the extent of its disclosures.

Those measures, ultimately rejected, included “hiring Kahn into the government so that certain criminal statues would apply if the work was published … undertaking ‘clandestine service applications’ against the author, which apparently meant anything from physical surveillance to a black-bag job; and conducting a ‘surreptitious entry’ into Kahn’s Long Island home,” Bamford wrote.

According to Bamford, Macmillan, Dr. Kahn’s publisher, submitted the entire manuscript to the Defense Department, which responded that “it would not be in the national interest to publish the book.” In the end, Macmillan and Dr. Kahn agreed only to delete several paragraphs relating to NSA’s cooperation with British intelligence.

Even when the popularity of Dr. Kahn’s book landed him on NBC’s “Tonight Show,” NSA employees were barred from acknowledging the existence of the volume.